Albeit I'm using a different phone @JTM185 I assume you mean the new Android ¹³ with Samsung One Ui 5.0.
I've just tried and in my Samsung Gallery Version 4.0.01.10
I assume your using the stock Samsung Gallery.
I have several folders I've created and they are allowing me to move photos from one to another without issue.
It might be worth clearing the cache of your Gallery via Settings, Apps, Gallery, Storage and clear cache.
If I can be of any further help then please don't hesitate. Take care. 😎
Daily Driver > Samsung Galaxy s²⁴ Ultra 512Gb ~ Titanium Black.
The advice I offer is my own and does not represent Samsung’s position.
I'm here to help. " This is the way. "
